JP2000013191A - Tv tuner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change over the reception of UHF signals and VHF signals without using a change-over switch and to simplify a circuit compared to a conventional one without deteriorating the passing characteristic of the signal. SOLUTION: A UHF signal passing part 110 and a VHF signal passing part 120 are connected in parallel to the post stage of a trap high pass filter part 100 where an unwanted signal is removed and UHF and VHF signals are caused to pass. In the UHF signal passing part 110, respective circuit constants are set as far as possible so that the circuit impedance does not become a value that affects the VHF signal passing part 120. In the VHF signal passing part 120, respective circuit constants are set as far as possible so that the circuit impedance does not become a value that affects the VHF signal passing part 120.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called TV tuner for selecting a television signal in a television receiver, a video tape recorder, or the like, and more particularly, to a circuit whose simplification and performance are improved. About.

[0002]

2. Description of the Related Art Conventionally, a so-called TV tuner switches between a UHF signal and a VHF signal. For example, in a so-called electronic tuning type, a so-called switching element such as a switching diode is used in its filter stage. One having a UHF / VHF switching circuit is known and well known. That is, as shown in FIG. 4, when a signal of both UHF and VHF is input from the input terminal 80, first, the input signal is changed by the UHF / VHF switching circuit 81. , Are input only to either the UHF system or the VHF system at the subsequent stage. UHF ・
Subsequent stages of the VHF switching circuit 81 include a so-called UHF system including a UHF tuning circuit 82 including a UHF filter (not illustrated) and a UHF amplifier 83, and a VHF tuning circuit 84 including a VHF filter (not illustrated) and a VHF tuning circuit 84. A so-called VHF system composed of the amplifier 85 is configured.

FIG. 5 shows a more specific configuration example of such a conventional TV tuner, in particular, a so-called filter stage. Hereinafter, this conventional circuit configuration example will be generally described with reference to FIG. Will be described. The filter stage of this tuner provides a UHF signal system to the input terminal 80 and a VH
F signal system is provided in parallel.
The F signal system includes a UHF filter unit 82A and a MOS FE
And a UHF amplifier unit 83 mainly composed of T86a. The VHF signal system includes a VHF filter unit 84A and a MOS FET 8
VHF amplifier section 85 composed mainly of 6b
It has what has. UHF filter section 8
2A includes a first diode 87 in series in its signal path.
a when the UHF signal is received, the voltage VB <
The voltage UB is set to a so-called ON state, so that a signal can be passed.

On the other hand, a second diode 87b is connected in parallel to the signal path of the VHF filter section 84A, and the second diode 87b is connected to a predetermined voltage UB when receiving a UHF signal. Is applied, and the circuit after the second diode 87b is set to a so-called shunt state, so that the transmission of the UHF signal to the subsequent stage is prevented. When the VHF signal is received, the first diode 87a is turned off, so that the VHF signal is not transmitted to a circuit subsequent to the first diode 87a.
7b is turned off, and the VHF signal is transmitted to the subsequent stage.

[0005]

However, in the conventional circuit described above, when the electric field strength of the received radio wave is large, the tuner section is close to the antenna, so that signal distortion is apt to occur. ), Double and triple harmonics are generated in the first and second diodes 87a and 87b, so that a so-called beat phenomenon is caused and the performance of the tuner unit is degraded. It was an inviting factor. As described above, in order to switch between the UHF signal and the VHF signal,
Inserting a diode so that operation control can be performed in a circuit not only complicates the circuit, but also leaks a high-frequency signal to a DC power supply system for controlling the operation of the diode, and generates a UHF signal and a VHF signal. And the spurious characteristics are deteriorated.
Further, if the signal switching and the so-called shunt circuit are simply deleted, the tuning circuit of the UHF signal and the tuning circuit of the VHF signal interfere with each other, failing to obtain a good pass characteristic in a desired pass band, and making unnecessary so-called so-called shunt circuits. There were problems such as the occurrence of traps and mismatch points.

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and is capable of receiving a UHF signal and a VHF signal without using a changeover switch. And a TV tuner that simplifies the above. It is another object of the present invention to provide a TV tuner in which a beat phenomenon unlike the related art caused by mixing of a signal in a specific frequency band does not occur. Another object of the present invention is to provide a TV tuner in which a high-frequency signal does not leak to a DC power supply system and mutual interference between a UHF signal and a VHF signal and spurious characteristics do not deteriorate. . Another object of the present invention is to improve reliability by simplifying a circuit.

[0007]

According to a first aspect of the present invention, there is provided a TV tuner for tuning and amplifying a UHF signal to an input terminal to which a high frequency signal including a UHF signal and a VHF signal is applied. A passing unit and a VHF signal passing unit for tuning and amplifying the VHF signal are connected in parallel, while a UHF signal passing unit for tuning and amplifying the UHF signal and a VHF signal passing unit for tuning and amplifying the VHF signal. UHF / VHF signal switching circuit for switching between the UHF signal and a VHF signal passing unit for tuning and amplifying the VHF signal when an input signal is applied to a UHF signal passing unit for tuning and amplifying the UHF signal The shunt circuit for shunting the signal path to the control circuit is not provided.

[0008] Such a configuration is particularly configured to omit a non-linear element such as a diode switch provided in an input stage for switching between reception of a UHF signal and reception of a VHF signal. Is simplified, signal distortion at the time of strong electric field input caused by a nonlinear element in the input stage is eliminated, and inconvenience caused by the signal distortion can be avoided. in this way,
The UHF signal passage section and the VHF signal passage section are connected in parallel to the input terminal without using a conventional switching element. It is preferable to select the respective circuit constants of the UHF signal passage section and the VHF signal passage section so as not to affect them. That is, regarding the interference of the respective tuning circuits of the UHF and VHF signals, the circuit constant of the VHF tuning circuit is set on the assumption that the UHF tuning circuit is connected in parallel at the time of VHF reception. V
Since it is necessary to be in a high impedance state with respect to the HF band, interference is avoided by using a circuit configuration having no so-called splitter circuit as in a conventional circuit. Also, at the time of UHF reception, the VHF tuning circuit is tuned to the high frequency range of the VHF band so that good pass characteristics can be obtained even in a circuit configuration having no so-called shunt circuit as in a conventional circuit. VHF
Preferably, interference from the tuning circuit is avoided.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The members, arrangements, and the like described below do not limit the present invention, and can be variously modified within the scope of the present invention. First, a schematic configuration of a TV tuner according to the present invention will be described with reference to FIG. FIG.
It shows a configuration of a main part of a V tuner, particularly, a part called a filter stage of a so-called electronic tuning tuner, and a later-stage frequency conversion circuit and the like are omitted. That is, the TV tuner according to the present invention uses the UHF signal and the VH
RF input terminal 70 to which a high-frequency signal including an F signal is applied
However, the UHF signal passing unit 110 and the VHF signal passing unit 120 are connected in parallel. In particular, in comparison with the conventional circuit (see FIG. 4), U
The HF / VHF switching circuit 81 (see FIG. 4) is not provided, and the input stage of the TV tuner is not provided with a so-called splitter circuit for separating the UHF signal and the VHF signal. is there. In addition,
The TV tuner in the present invention is used not only in a so-called TV receiver, but also in a so-called VTR (Video
tape recorder).

Next, a more specific first circuit configuration example will be described with reference to FIG. FIG. 1 also shows a configuration of a so-called filter stage of a so-called electronic tuning tuner, similarly to FIG. 3 described above, and the subsequent-stage frequency conversion circuit and the like are omitted. The filter stage of this electronic tuning tuner includes a trap high-pass filter section 100.
, UHF signal passing unit 110 and VHF signal passing unit 12
0. The trap / high-pass filter unit 100 is provided at the head of this filter stage, and the UHF signal passing unit 110 and the VHF signal passing unit 120 are arranged in parallel with the output stage of the high-pass filter 102 in the subsequent stage. It has a connected configuration. A mixing circuit, a local oscillation circuit (not shown), and the like are provided at a stage subsequent to the UHF signal passing unit 110 and the VHF signal passing unit 120, so that a predetermined video intermediate frequency is output. .

The trap / high-pass filter section 100 includes:
The trap circuit 101 includes a trap circuit 101 and a high-pass filter 102. The trap circuit 101 includes an IF (Intermedi
atefrequency) band, and is provided in series on the signal path. That is, a first capacitor (denoted as “C1” in FIG. 1) 1 and a first coil (denoted as “L1” in FIG. 1) 21 are connected in parallel, and the whole is connected to a signal path. They are inserted in series. The RF signal input terminal 70 receives a high-frequency signal received by an antenna (not shown). The high-pass filter 102 removes an unnecessary low-frequency component signal such as a so-called CB band and passes only a necessary high-frequency band signal. The high-pass filter 102 in the first circuit configuration example includes a second capacitor (indicated as “C2” in FIG. 1) 2 inserted in series with a signal path, and an input terminal of the second capacitor 2. On the (end on the side of the trap circuit 101) side, a second coil ("L" in FIG. 1) connected to the ground.
2) and the output terminal (U
A third coil (denoted as "L3" in FIG. 1) 23 connected between the HF signal passage portion 110 and the VHF signal passage portion 120 (the end connected to the VHF signal passage portion 120) and the ground.
And is constituted by

The UHF signal passing section 110 includes a UHF tuning circuit 111 and a UHF signal amplifier ("A" in FIG. 1).
MP1 ”) 112). The UHF tuning circuit 111 first outputs the output terminal of the high-pass filter 102, in other words, UHF / VHF
One end of a third capacitor (referred to as "C3" in FIG. 1) 3 is connected to the signal branch point 71, and the other end of the third capacitor 3 is connected to a fourth coil ("L" in FIG. 1).
4) 24). And the fourth
The other end of the coil 24 is connected to one end of a fifth capacitor (denoted as "C5" in FIG. 1) 5, and the other end of the fifth capacitor 5 is connected to the input end of the UHF signal amplifier 112. Have been.

A fifth coil (denoted as "L5" in FIG. 1) 25 is connected between the connection point between the fourth coil 24 and the fifth capacitor 5 and the ground. A first variable capacitance diode (in FIG. 1, "VD
1) and a fourth capacitor (denoted as "C4" in FIG. 1) 4 are connected in series. That is, the anode of the first variable capacitance diode 62 is connected to the connection point between the fourth coil 24 and the fifth capacitor 5, and the fourth variable capacitance diode 61 is connected between the cathode of the first variable capacitance diode 61 and the ground. The capacitor 4 is connected. Further, the UHF tuning voltage V _UTU is applied to the cathode of the first variable capacitance diode 61 via a second resistor (denoted as “R2” in FIG. 1). . The third capacitor 3, the fourth and fifth coils 24 and 25, the first variable capacitance diode 61 and the fourth
Is a tuning circuit for the UHF signal, and by changing the magnitude of the UHF tuning voltage V _UTU , the first variable capacitance diode 61
Is changed to adjust the tuning frequency.

The VHF signal passing section 120 includes a VHF tuning circuit 121 and a VHF signal amplifier (in FIG. 1, "A
MP2 ”) 122). The VHF tuning circuit 121 is configured such that one end of a seventh coil (denoted as “L7” in FIG. 1) 27
While connected to the F / VHF signal branch point 71, the other end is connected to an eighth coil (denoted as "L8" in FIG. 1).
8 is connected to one end. Then, the eighth coil 28
Is connected to a tenth capacitor ("C1" in FIG. 1).
The other end of the tenth capacitor 10 is connected to an eleventh coil (described as “L11” in FIG. 1). Furthermore, the first
The other end of the first coil 31 is connected to a second variable capacitance diode (denoted as “VD2” in FIG. 1) 62 and a third variable capacitance diode (denoted as “VD3” in FIG. 1) 6
3, the second variable capacitance diode 6
2 is connected to the VHF signal amplifier 12 via an eleventh capacitor (denoted as “C11” in FIG. 1) 11.
2, the anode of the third variable capacitance diode 63 is connected to ground, respectively. Also, UH
A sixth capacitor (denoted as “C6” in FIG. 1) 6 is connected between the F / VHF signal branch point 71 and the anode of the second variable capacitance diode 62.
Between the anode of the variable capacitance diode 62 and the ground,
A sixth resistor (denoted as “R6” in FIG. 1) 46 is connected.

On the other hand, a seventh capacitor (denoted as "C7" in FIG. 1) 7 is connected in parallel to the eighth coil 28, and the first and second capacitors 7 are connected to each other with anodes. Diodes ("D1" in FIG. 1 respectively)
) And 52 are connected in parallel to the eighth coil 28. That is, the cathode of the second diode 52 is connected to the connection point between the eighth coil 28 and the seventh coil 27, and the cathode of the first diode 51 is connected to the connection point of the eighth coil 28 and the tenth capacitor 10. Each is connected to a connection point. Further, a ninth coil (denoted as “L9” in FIG. 1) 29 and an eighth capacitor (denoted as “C8” in FIG. 1) 8 are provided between the cathode of the second diode 52 and the ground. Are connected in series, and a connection point between the ninth coil 29 and the eighth capacitor 8 is connected to a fourth resistor (“R” in FIG. 1).
2) 44, the VHF band switching control voltage V _B1 is applied. That is, this V
When the HF band switching control voltage V _B1 is set to a voltage higher than a predetermined value enough to make the first and second diodes 51 and 52 non-conductive, the first and second diodes 51 and 52 become non-conductive. , The seventh coil 27 and the eighth coil 2
8 are connected in series. Then, in this state, it is tuned to the low frequency band of the VHF band, and is ready to receive the low frequency band of the VHF band.

The first and second diodes 51, 5
A tenth coil (denoted as "L10" in FIG. 1) 30 and a ninth capacitor (denoted as "C9" in FIG. 1) 9 are connected in series between the anode 2 and the ground. . A connection point between the tenth coil 30 and the ninth capacitor 9 is connected to a fifth resistor (“R” in FIG. 1).
5) VHF band switching control voltage V via 45
_B2 is applied. That is, when the voltage V _B2 is set to a voltage higher than a predetermined value enough to make the first and second diodes 51 and 52 conductive, the eighth coil 28 is short-circuited and the seventh coil 27 Is
The state is directly connected to the tenth capacitor 10. In this state, it is tuned to the high frequency band of the VHF band, and the high frequency band of the VHF band can be received. On the other hand, VHF is connected to the cathodes of the second and third variable capacitance diodes 62 and 63 via a seventh resistor (denoted as “R7” in FIG. 1) 47.
The tuning voltage V _VTU is applied. By changing the voltage V _VTU , the capacitance of the second and third variable capacitance diodes 62 and 63 changes, thereby changing the tuning frequency. Thus, a VHF signal having a predetermined frequency according to the magnitude of the voltage V _VTU is input to the VHF amplifier 122.

Next, the operation in this configuration will be described. First, in the case of receiving a UHF signal, the VHF signal passing section 120 is in a state of being tuned to the high band of the VHF band.
That is, the VHF band switching control voltage V _B2 is set to V _B2 > V
_B1 is set, the first and second diodes 51 and 52 are turned on, and the eighth coil 28 is short-circuited.
This is because the so-called circuit constants of the respective circuit elements of the UHF signal passing unit 110 take into account the impedance to the UHF signal viewed from the UHF signal passing unit 110 when the VHF signal passing unit 120 is in the high-band reception state. This is because the setting of the circuit constant is considered so that the impedance of the VHF signal passing unit 120 with respect to the UHF signal viewed from the UHF signal passing unit 110 is increased in this case. By adjusting the UHF tuning voltage V _UTU as in the conventional circuit,
A desired UHF signal can be selected, and the selected signal is amplified by the UHF signal amplifier 112 and output to the subsequent stage.

On the other hand, at the time of receiving the VHF signal, if the desired VHF signal is on the high frequency side, the VHF band switching control voltage V _B2 is set to V _B2 > V _B1 and the high frequency receiving state is set. If the desired VHF signal is on the low frequency side, the VHF band switching control voltage V _B1 is set to V _B1 > V _B2 , and the low frequency reception state is set. Here, in any receiving state, VHF
Since the impedance of the UHF signal passing unit 110 viewed from the signal passing unit 120 is considered when setting each circuit constant, the VH signal is received when the VHF signal is received.
For the operation of the F signal passing unit 120, the UHF signal passing unit 1
10 has no effect. And
As in the conventional circuit, a desired VHF signal can be selected by adjusting the VHF tuning voltage V _VTU , and the selected signal is amplified by the VHF signal amplifier 122 and output to the subsequent stage. Becomes

As described above, the so-called circuit constants of the respective circuit elements of the UHF signal passing section 110 and the VHF signal passing section 120 are, in the related art, the optimum circuit constants in the UHF signal receiving state. The VHF signal passing unit 120 sets the optimum circuit constants independently in the VHF signal receiving state without considering each other's circuit constants, whereas in this circuit configuration example, the UHF signal passing unit The impedance of the VHF signal passing section 120 with respect to the UHF signal viewed from 110 is increased, and the VHF viewed from the VHF signal passing section 120 is increased.
The so-called circuit constants of the UHF signal passing unit 110 and the VHF signal passing unit 120 are set such that the impedance of the UHF signal passing unit 120 for the signal is high. Therefore, as described above, unlike the related art, the UHF signal reception by the so-called switching element and the VHF
Switching to signal reception is not necessary.

Next, a second example of the circuit configuration will be described with reference to FIG. Note that the same components as those in the first circuit configuration example shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. Hereinafter, different points will be mainly described. . First, the difference of the circuit configuration from the first circuit configuration example will be described. One end of the third coil 23 is connected via a fourteenth capacitor (denoted as “C14” in FIG. 1) 14. It is connected to earth. Further, the third coil 23 and the first
4 is connected to the first resistor (FIG. 1).
In this case, an operation control voltage V for controlling the operation of a third diode 53, which will be described later, is supplied via an “R1” 41).
_CON is applied.

The UHF / VHF signal branch point 71 and V
Between the HF signal passage section 120, a trap circuit 130 for FM interference countermeasures is inserted. That is, this FM
The trap circuit 130 for countermeasures against interference particularly has an F of 88 to 93 MHz when receiving 6 channels (83.25 MHz).
To remove interference caused by M radio broadcast signals,
When a six-channel television signal is received, an FM radio broadcast signal that causes reception interference is trapped here. Specifically, the third diode 53 is connected between the UHF / VHF signal branch point 71 and the VHF
In series with the signal passing unit 120, the anode is VH
It is provided so as to be on the F signal passing section 120 side. Then, the twelfth and thirteenth capacitors connected in series (in FIG. 1, denoted as “C12” and “C13”, respectively)
12 and 13 are connected in parallel to the first diode 51. Further, a sixth coil (denoted as “L6” in FIG. 1) 26 is connected to the thirteenth capacitor 13 in parallel. Further, a third resistor (indicated as “R3” in FIG. 2) 43 is connected in parallel to the eighth coil 28 in order to adjust the circuit impedance due to the provision of the above-described trap circuit 130 for countermeasures against FM interference. It is connected.

In such a configuration, in a state other than the six-channel reception, the operation control voltage V _CON applied through the first resistor 41 is equal to or less than a predetermined value enough to make the third diode 53 conductive. Voltage level.
As a result, the third diode 53 becomes conductive, and
Therefore, the FM interference countermeasure trap circuit 130 is short-circuited, and the signal appearing at the UHF / VHF signal branch point 71 is input to the VHF signal passing unit 120 without passing through the FM interference countermeasure trap circuit 130. Become.
On the other hand, when the operation control voltage V _CON is set to a voltage level equal to or higher than a predetermined value enough to make the third diode 53 non-conductive, the third diode 53 becomes non-conductive, so that it is possible to prevent FM interference. The short circuit state of the trap circuit 130 is eliminated, the FM interference countermeasure trap circuit 130 becomes effective, and a predetermined FM radio broadcast signal is trapped here. Here, it is preferable that the operation control voltage V _CON is generated by a drive circuit (not shown) based on a control signal from a microcomputer (not shown), for example.

The operation of the entire circuit is basically the same as that of the first circuit configuration example shown in FIG. 1 except for the above-described trap circuit 130 for countermeasures against FM interference. The detailed description is omitted here.

[0023]

As described above, according to the present invention,
Conventionally, in a TV tuner, a desired UHF signal or VHF signal can be received without using a switching circuit including a diode switch or the like provided in an input stage for switching between a UHF signal and a VHF signal. With this configuration, the conventional switching circuit becomes unnecessary, the circuit configuration can be simplified, and the reliability of the entire circuit can be improved by reducing the number of components. In addition, a non-linear element such as a diode switch is not required in the input stage for switching between the reception of the UHF signal and the reception of the VHF signal.
It is possible to avoid the occurrence of signal distortion at the time of inputting a so-called strong electric field, and it is possible to eliminate various phenomena caused by signal distortion that may cause deterioration of the characteristics of the TV tuner. Further, as described above, a diode switch for switching between the reception of the UHF signal and the reception of the VHF signal is not required. Therefore, unlike the related art, the UHF signal and the VHF signal via the DC power supply for controlling the diode switch are different. Mutual interference with signals can be avoided, and the performance can be further improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first circuit configuration example of a filter stage of a TV tuner according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second circuit configuration example of the filter stage of the TV tuner according to the embodiment of the present invention.

FIG. 3 is a block diagram of a filter stage of the TV tuner according to the embodiment of the present invention.

FIG. 4 is a block diagram of a filter stage of a conventional TV tuner.

FIG. 5 is a circuit diagram showing a circuit configuration example of a filter stage of a conventional TV tuner.

[Explanation of symbols]

 Reference numeral 70: RF input terminal 100: Trap / high-pass filter unit 101: Trap circuit 102: High-pass filter 110: UHF signal passing unit 111: UHF tuning circuit 112: UHF signal amplifier 120: VHF signal passing unit 121: VHF tuning circuit 122: VHF signal amplifier 130: FM interference countermeasure trap circuit

Claims (4)

[Claims] 1. A UHF signal passing unit that tunes and amplifies a UHF signal to an input terminal to which a high-frequency signal including a UHF signal and a VHF signal is applied, and a VHF signal passing unit that tunes and amplifies a VHF signal. And a UHF / VHF signal switching circuit that switches between a UHF signal passing unit that tunes and amplifies the UHF signal and a VHF signal passing unit that tunes and amplifies the VHF signal, and the UHF signal In a state where an input signal is applied to a UHF signal passage section for performing tuning and amplification of
A TV tuner characterized by not having a shunt circuit for shunting a signal path to a VHF signal passage section for tuning and amplifying an HF signal. 2. The TV tuner according to claim 1, wherein a high-pass filter is provided between the UHF signal passing section and the VHF signal passing section and the input terminal. 3. The TV tuner according to claim 1, wherein a splitter circuit for separating a UHF signal and a VHF signal is not provided. 4. A VHF signal passing section includes: a VHF tuning circuit having a tuning circuit for a VHF signal;
And a VHF amplifier for amplifying the output of the tuning circuit for F. The tuning circuit for VHF has two coils connected in series for tuning to a VHF signal. One end is connected to the cathode of the first diode, and the other end is connected to the cathode of the second diode. The first and second diodes have their anodes connected to each other. When the voltage of is applied,
When the first and second diodes are turned on, the one of the coils is short-circuited, and a high-frequency reception state in the VHF band is set. When a voltage is applied, the first and second diodes are turned off so that the one coil is turned off and the VHF band low-band reception state is set. The TV tuner according to claim 1, 2 or 3, wherein the TV tuner is provided.